I'm trying to create a singleton object with parameters which are specified by runtime. Example:
object NetworkPusher {
val networkAdress = ???
...
}
Imagine the networkAdress param comes from the command-line. How can I make a workaround to do this?
Singletons are initialized lazily.
scala> :pa
// Entering paste mode (ctrl-D to finish)
object Net {
val address = Config.address
}
object Config { var address = 0L }
// Exiting paste mode, now interpreting.
defined object Net
defined object Config
scala> Config.address = "1234".toLong
Config.address: Long = 1234
scala> Net.address
res0: Long = 1234
FWIW.
:pa paste mode! Great tip!This is rather convention over configuration approach. But it is thread safe and adds obligatory initialisation requirement:
abstract class NetworkPusher() {
private var networkAddress: String = ""
def setNetworkAddr(addr: String) = networkAddress = addr
def getNetworkAddr() = networkAddress
}
object NetworkPusherFactory {
private var initOnceReady: NetworkPusher => Unit = _
private lazy val initializedInstance = {
val pusher = new NetworkPusher(){}
initOnceReady(pusher)
pusher
}
def create(init: NetworkPusher => Unit): NetworkPusher = {
initOnceReady = init
initializedInstance
}
}
object Main {
def main(args: Array[String]): Unit = {
val networkAddr = "A.D.D.R" // args[0]
val onePusher = NetworkPusherFactory.create(
instance => instance.setNetworkAddr(networkAddr)
)
println(s"using ${onePusher.getNetworkAddr}")
}
}
Using lazy:
object Program {
var networkAdress: String = _
def main(args: Array[String]): Unit = {
networkAdress = args(0)
println(NetworkPusher.networkAdress)
}
object NetworkPusher {
lazy val networkAdress = Program.networkAdress
}
}
